How would you describe this eating motion

And yes, it's important. A big armored worm eats a monster like this. And can you do it in a single sentence? (NOTE: I won't be using this. Just want to see how you would describe it and how you see it so I can write my own sentence.)

Well, the descriptions above both avoid Xenomorph and disarticulation...i'll give it a shot...

Its mouth opened, teeth, row upon row of them, jutting up like razors on needles. Its prey drew back, but then the whole mouth, like it was a thing detached, raced forward and engulfed the helpless prey. An instant of teeth rushing forward, and then nothing but a worm looking for its next prey.

Maybe you could call it like a Phronima Parasite, that is the creature the xenomorph is based on.

Silence emerged as the shark glided across the deep vault, his ship-sized body sailing proudly. All power, all cunning. King of the Sea. This silence was soon interrupted as the shark propelled his weight forward and gouged those fangs into the fish’ limbs.